Problem: In chemistry class, the girl to boy ratio is $7$ to $6$. If there are a total of $65$ students, how many girls are there?
Explanation: A ratio of $7$ girls to $6$ boys means that a set of $13$ students will have $7$ girls and $6$ boys. A class of $65$ students has $5$ sets of $13$ students. Because we know that there are $7$ girls in each set of $13$ students, the class must have $5$ groups of $7$ girls each. There is a total of $35$ girls in chemistry class.